SARS-CoV-2 Spike S1-specific IgG kinetic profiles following mRNA or vector-based vaccination in the general Dutch population show distinct kinetics

mRNA- and vector-based vaccines are used at a large scale to prevent COVID-19. We compared Spike S1-specific (S1) IgG antibodies after vaccination with mRNA-based (Comirnaty, Spikevax) or vector-based (Janssen, Vaxzevria) vaccines, using samples from a Dutch nationwide cohort. In adults 18–64 years old (n = 2412), the median vaccination interval between the two doses was 77 days for Vaxzevria (interquartile range, IQR: 69–77), 35 days (28–35) for Comirnaty and 33 days (28–35) for Spikevax. mRNA vaccines induced faster inclines and higher S1 antibodies compared to vector-based vaccines. For all vaccines, one dose resulted in boosting of S1 antibodies in adults with a history of SARS-CoV-2 infection. For Comirnaty, two to four months following the second dose (n = 196), S1 antibodies in adults aged 18–64 years old (436 BAU/mL, IQR: 328–891) were less variable and median concentrations higher compared to those in persons ≥ 80 years old (366, 177–743), but differences were not statistically significant (p > 0.100). Nearly all participants seroconverted following COVID-19 vaccination, including the aging population. These data confirm results from controlled vaccine trials in a general population, including vulnerable groups.


Boosting of infection-induced antibodies irrespective of COVID-19 vaccine. In adults aged
18-64, S1 IgG concentrations were higher in persons with a history of SARS-CoV-2 after one vaccine dose compared to previously naive persons after a completed schedule irrespective of vaccine type ( Fig. 2A). For persons with an infection history, no further increases were seen after a second dose if applicable (p > 0.100).

Discussion
In response to the global COVID-19 pandemic, novel vaccine strategies using mRNA-and vector-based induction of the immune system have been developed. In adults aged 18-64, we observed the steepest inclines and highest Spike S1 IgG concentrations up to 2 months following vaccination with mRNA-based vaccines compared to vector-based COVID-19 vaccines. Boosting of Spike S1 IgG responses in persons with a history of infection was seen for all four vaccines, and a second dose did not further increase anti-S1 IgG levels. We used antibody concentration units according to the WHO international standard, enabling direct comparison between studies.
Others have shown that IgG to Spike S1 following SARS-CoV-2 infection or mRNA vaccination shows an initial decline with stabilization of IgG antibodies after 4-6 months 11 . The rapid induction of high levels of antibodies by mRNA vaccines, compared to vector-based vaccines, followed by an early decay may point to the induction of short-lived plasma blasts by the mRNA vaccines that disappear soon after the immunization, and may not predict the number of sustaining memory cells [12][13][14][15] .
During the delta variant period in the Netherlands, overall VE against hospitalization was 91% for Comirnaty, 96% for Spikevax, 88% for Vaxzevria and 82% for Janssen 1 . Antibody data from our study mirrored these trends which supports the notion that antibody binding and neutralization correlate with vaccine efficacy 16 . However, the relative difference in VE estimates is smaller than in antibody levels, indicating that antibody levels alone do not constitute immune protection, as expected. As time since vaccination elapse, VE and antibody concentrations decrease. The observed reduction in antibody levels and vaccine effectiveness in the population underline the need to boost the immune response with an additional vaccine dose, especially for vulnerable persons. No   Figure 1. Spike S1 immunoglobulin G (IgG) kinetics following COVID-19 vaccination by number of doses and vaccine brand in SARS-CoV-2-naive adults aged 18 to 64 years old. The dashed horizontal line represents the threshold for seropositivity. Data for Janssen is duplicated across the two panels to enable direct comparison with the other vaccine brands after one dose and a completed vaccination schedule. For comparison, IgG concentrations following a positive SARS-CoV-2 PCR or antigen test in unvaccinated participants are shown alongside vaccination responses; data is duplicated in both panels (for details see Supplementary Table S3). Fit and 95% confidence bands are shown from a Generalized Additive Model, using penalized splines, with only time since dose in days as explanatory variable. For results of multivariable models, see Supplementary Table S1. BAU/mL: binding antibody units per mL; IgG: immunoglobulin G. www.nature.com/scientificreports/ correlate of protection has been defined for any of the SARS-CoV-2 variants. However a third vaccine dose has been shown to increase antibody levels and protection against disease caused by different variants [17][18][19] . More specifically, a third vaccine dose seems to be important for increased neutralization towards the Omicron variant 20,21 .
Boosting of S1 IgG after one dose of mRNA or vector vaccine in previously infected persons has been described previously 5,22 . Here we confirm boosting of infection-induced immune memory regardless of vaccinetype. This boosting seems stronger than observed after revaccination, indicating a more matured underlying memory B cell response induced by viral infection compared to immunization. This observation needs in-depth follow-up in the future when the opposite will occur: boosting of vaccine-induced immunity by infection.
We showed highly variable antibody response between individuals which increased in community-dwelling elderly aged 80 years and older after completion of Comirnaty. To date, most of the humoral data in the elderly are from nursing home residents 23 . Müller et al. showed lower antibody profiles in nursing home residents compared to those 20-60 year old shortly following vaccination, which contrast with our findings. Such discrepancies might be caused by the increased age range (up to 91 in our study versus 100 in Müller et al.), presence of more complex comorbidities or the fact that antibody production is delayed in the elderly.
The data presented here are a highly relevant confirmation of results from controlled vaccine trials since we show high immunogenicity after vaccination in the general population, including vulnerable groups and different vaccination regimens. Although most persons seroconverted regardless of the vaccine received, mRNA-and vector-based COVID-19 vaccines induced distinct S1-specific IgG kinetic profiles. Further exploration of the translation of antibody quantity to antibody quality and subsequent protection against infection and (severe) disease as well as the involvement of other immune compartments such as T cells is needed.

Methods
Study population. We used samples from a four-monthly prospective nationwide cohort study in the Netherlands which has been described in detail elsewhere 7,8 . Participants provided a fingerprick blood sample and completed a questionnaire including sociodemographic factors, comorbidities, COVID-19 disease (symptoms, type and date of SARS-CoV-2 test) and COVID-19 vaccination (brand and dates). Participants 18 years or older who had received one or two doses of Comirnaty, Spikevax, Vaxzevria or Janssen were selected. Unvaccinated participants aged 18-64 years old who reported a positive SARS-CoV-2 PCR or antigen test up to two Figure 2. Violin plots of Spike S1 immunoglobulin G (IgG) concentrations by number of COVID-19 vaccine doses, SARS-CoV-2 infection history and vaccine brand (A) and in SARS-CoV-2-naïve adults at two to four months following a completed Comirnaty schedule by age group (B). Triangles and black horizontal lines represent median concentrations of IgG to Spike S1 in BAU/mL. The dashed horizontal line represents the threshold for seropositivity. In (A) IgG measurements were taken between two weeks and two months after the indicated dose; while in (B) between two and four months after completion of the Comirnaty schedule. Wilcoxon-Mann-Whitney tests were used to test for differences in IgG concentrations by infection history in (A) with blocking for strata of sex, and by age group in (B) with blocking for strata of sex and time since second dose (less versus more than three months). * p < 0.05; ** p < 0.01; *** p < 0.001; NS: not significant (p > 0.100); BAU/mL: binding antibody units per mL; IgG: immunoglobulin G. Antibody detection. Serum samples were analyzed for IgG concentrations to SARS-CoV-2 Spike S1 using a previously described bead-based assay 9 . IgG concentrations were expressed in binding antibody units (BAU/ mL) using the NIBSC 20/136 WHO standard 10 .
Statistical analyses. Statistical analyses were done in R Studio (version 4.1.0) 24 . Mann-Whitney tests were used to compare IgG concentrations by age group with blocking per strata of sex and time since vaccination (dichotomized as more or less than 3 months), and by infection history with blocking per strata of sex (coin 25 ). IgG kinetics were fitted with a Generalized Additive Model, using penalized splines (mgcv 26 ).
Ethics declaration. The study was ethically approved by the Medical research Ethics Committees United (MEC-U), the Netherlands (Clinical Trial Registration NL8473). All participants gave written informed consent. All research was performed in accordance with the relevant guidelines and regulations. www.nature.com/scientificreports/